We all agree that teachers can make a tremendous difference in the lives of students, and we all can remember a great teacher who was important in our own lives. The challenge is to identify more great teachers. Value-added measures, which rate teachers based on their impacts on students’ test scores, can help us do so. Our recent study shows that when a high-value-added teacher enters a school, test scores for students in the grade taught by that teacher rise immediately (as shown in the figure below). And the gains don’t stop there: the students who learn from that teacher are more likely to attend college, earn more, and are less likely to have children as teenagers. Even when new teachers are evaluated with just a few years of data, those who get high value-added ratings produce large gains for their students.

When a high-value-added teacher (in the top 5 percent) enters a school, end-of-school-year test scores in the grade he or she teaches rise immediately.

While our findings show that improving teacher value-added would have large returns for students, it’s less clear how to achieve this goal in practice. One problem is that evaluating teachers using test scores could encourage counterproductive behaviors, such as teaching to the test or even cheating. These responses may reduce — but are unlikely to completely eliminate — the benefits of using test scores for evaluation. The best way to rate teachers most likely combines test score value-added ratings with other information, like principal or peer evaluations based on classroom observation.

More generally, we should recognize that value-added data can be a useful statistic even though it’s not perfect, just like performance measures in other occupations. The manager of a baseball team pays attention to a player’s batting average even though it too is an imperfect statistic that bounces around over time. If a new player gets no hits in his first month, one option is waiting to see whether he is just in a temporary slump. Another is more coaching. But on occasion, the best option may be to let that player go and call up a replacement.

Few insist on equity irrespective of performance, both in sports and many other professions, so why would this be the norm in teaching? The stakes in teaching are much larger than winning or losing a game; teachers impact hundreds of children over their careers. Teaching should be recognized and rewarded as an elite profession, one which attracts and retains the most talented stars. When combined with other measures of teacher performance, objective data on test score value-added can help us find the star teachers who will shape the next generation.